1. Field of the Invention
The present invention relates to a cleaning apparatus for cleaning workpieces, such as semiconductor wafers or glass substrate for LCDs.
2. Description of the Related Art
Generally, a cleaning apparatus is employed prevalently in a semiconductor device fabricating process. The cleaning apparatus carries workpieces, such as semiconductor wafers or glass substrate for LCDs, (hereinafter referred to as xe2x80x9cwafersxe2x80x9d) sequentially to cleaning tanks respectively containing chemical liquids and rinsing liquids for cleaning and the like. A known cleaning apparatus shown in FIG. 13 has a cleaning tank c having an inner tank a containing a cleaning liquid L in which wafers W are immersed and an outer tank b surrounding an upper end part of the inner tank a. A circulation line f connecting cleaning liquid supply nozzles d disposed in a lower part of the inner tank a and a drain port e formed in a bottom wall of the outer tank b is provided, for example, with an air bellows circulating pump g, a damper h and a filter i. Wafers W held on a wafer boat j are immersed in the cleaning liquid L contained in the inner tank a of the cleaning apparatus, the cleaning liquid L is supplied from a cleaning liquid source into the inner tank a so that the cleaning liquid L overflows the inner tank a into the outer tank b. The cleaning liquid L overflowed into, the outer tank b is filtered and circulated. The wafers W are thus cleaned.
As the cleaning liquid is used repeatedly, contaminative particles, such as particles removed from the wafers W, are accumulated in the cleaning liquid. The wafers subjected to cleaning in the cleaning liquid are contaminated, the yield of the cleaning process is reduced and the cleaning performance of the cleaning apparatus is reduced if the particle concentration of the cleaning liquid exceeds a predetermined level.
As shown in FIG. 13, a branch line k for quality testing is connected to a part of the circulation line f on the discharge side of the circulating pump g, a testing means, for example, a particle counter m, is connected to the branch line k, and the discharge side of the particle counter m is connected to the outer tank b. A portion of the cleaning liquid L contained in the inner tank a is sampled and the number of particles contained in the sample cleaning liquid is measured to monitor the number of particles contained in the predetermined quantity of cleaning liquid L. In FIG. 13, indicated at n is a shutoff valve placed in the circulation line f, at p is a drain pipe connected to a drain port q formed in the bottom wall of the inner tank a, and at r is a drain valve placed in the drain pipe q.
Since the circulating pump g is of an air bellows type, the flow rate of the sample cleaning liquid is unstable and, consequently, accurate measurement of particles cannot be achieved. Since the circulating pump g serves also as means for supplying the cleaning liquid to the particle counter m, the cleaning liquid is supplied at a flow rate exceeding the ability of the particle counter m. Furthermore, since the measurement of particles uses the sample cleaning liquid sampled at a part of the circulation line f on the discharge side of the circulating pump g, the particle counter m adds the number of particles produced by the circulating pump g to the number of particles originally contained in the cleaning liquid and, consequently, the number of particles originally contained in the cleaning liquid cannot accurately be measured.
The present invention has been made in view of the foregoing problems and it is therefore an object of the present invention to provide a cleaning apparatus capable of accurately measuring fine contaminative particles, such as particles contained in a cleaning liquid, of operating at an improved yield and of exercising improved cleaning performance, and to provide a cleaning method to be carried out by the cleaning apparatus.
The foregoing object can be achieved by the followings.
According to one aspect of the present invention, a cleaning apparatus comprises a cleaning tank for containing a cleaning liquid in which workpieces are immersed for processing, a circulation line connected to the cleaning tank and provided with a filtering device, and a measuring line separate from the circulation line, provided with a fixed-quantity delivery means and a measuring means for measuring fine contaminative particles, such as particles, contained in the cleaning liquid and having a suction end connected to the cleaning tank.
In the cleaning apparatus of the present invention, the measuring means may be connected to the suction side of the fixed-quantity delivery means.
In the cleaning apparatus of the present invention, the measuring means may be connected to the discharge side of the fixed-quantity delivery means.
The measuring means is able to measure fine contaminative particles, such as particles, contained in the cleaning liquid accurately because a fixed quantity of the cleaning liquid can be taken out from the cleaning tank.
The cleaning apparatus of the present invention may be provided with a control means for synchronously operating the fixed-quantity delivery means and the measuring means.
The control means makes the measuring means carry out a measuring operation while the fixed-quantity delivery means is in suction operation.
A fixed quantity of the cleaning liquid can be sampled from the cleaning tank and the measuring means is able to achieve the accurate measurement of the fine contaminative particles, such as particles, contained in the cleaning liquid. The synchronous operation of the fixed-quantity delivery means and the measuring means improves measuring accuracy.
In the cleaning apparatus, the discharge end of the measuring line may be connected to the cleaning tank.
When the discharge end of the measuring line is connected to the cleaning tank, the sample cleaning liquid can be returned to the cleaning tank for the effective use of the cleaning liquid.
In the cleaning apparatus of the present invention, the cleaning tank may have an inner tank in which workpieces are immersed in the cleaning liquid, and an outer tank for containing the cleaning liquid overflowed the inner tank, and the suction side of the measuring line may be connected to the inner tank.
When the cleaning apparatus is thus constructed, a fixed quantity of the cleaning liquid contained in the inner tank in which workpieces are immersed in the cleaning liquid can be sampled and fine contaminative particles, such as particles, contained in the cleaning liquid can accurately be measured by the measuring means.
In the cleaning apparatus of the present invention, the discharge side of the measuring line may be connected to the outer tank.
When the discharge side of the measuring line is connected to the outer tank, the sample cleaning liquid subjected to measurement can be discharged into the outer tank instead of directly returning the same into the inner tank in which the workpieces are immersed in the cleaning liquid. Accordingly, the cleaning ability of the cleaning liquid is not reduced and the cleaning liquid can be circulated for the effective use of the same.
In the cleaning apparatus the present invention, the fixed-quantity delivery means may be a motor-operated bellows pump comprising a corrosion-resistant and chemical-resistant bellows, and a ball screw mechanism for driving the bellows.
The use of the chemical-resistant, durable motor-operated bellows pump capable of pumping a fixed quantity of the cleaning liquid extends the life of the apparatus, and improves measuring accuracy and the reliability of the apparatus.
In the cleaning apparatus of the present invention, the fixed-quantity delivery means may comprise a plurality of motor-operated bellows pumps arranged in parallel and the bellows pumps may be driven so that the bellows pumps operate in different phases, respectively.
When the motor-operated bellows pumps excellent in ability to pump a fixed quantity of fluid, chemical resistance and durability are employed the fixed-quantity delivery means, the life of the apparatus can be extended, measuring accuracy can be improved, the reliability of the apparatus can be enhanced, and fine contaminative particles, such as particles, contained in the cleaning liquid can accurately and continuously be measured.
In the cleaning apparatus of the present invention, the control means may provide a detection signal when the contaminative particle number of the cleaning liquid determined on the basis of measured data provided by the measuring means exceeds a predetermined upper limit value.
According to another aspect of the present invention, a cleaning method which immerses workpieces in a cleaning liquid contained in a cleaning tank and circulates the cleaning liquid contained in the cleaning tank through a circulation line provided with a filtering device for filtering the cleaning liquid comprises a step of sampling a fixed quantity of the cleaning liquid from the cleaning tank by a fixed-quantity delivery means, a step of measuring fine contaminative particles contained in the cleaning liquid sampled by the fixed-quantity delivery means by a measuring means, and a step of providing a detection signal representing the contaminative particle number of the cleaning liquid determined on the basis of measured data measured by the measuring means by a control means.
The control means of the present invention may provide a cleaning liquid change request signal when the contaminative particle number of the cleaning liquid on the basis of measured data provided by the measuring means exceeds a predetermined upper limit value.
The control means of the present invention may compare the contaminative particle number of the cleaning liquid sampled before a start of a first cleaning cycle and that of the cleaning liquid sampled after the completion of a cleaning cycle, and may provide the detection signal when a differential particle number between the respective contaminative particle numbers of the cleaning liquids, exceeds a predetermined upper limit value.
The control means of the present invention may provide an abnormal workpiece signal when the contaminative particle number on the basis of the measured data provided by the measuring means exceeds a predetermined upper limit value.
According to the present invention, a fixed quantity of the cleaning liquid can be sampled from the cleaning liquid contained in the cleaning tank at a sampling position other than the circulation line before staring a cleaning process or during a cleaning process, and the quantity of contaminative particles contained in the cleaning liquid is measured. Therefore, contaminative particles contained in the cleaning liquid can accurately be measured, and it is possible to inform the operator of an inappropriate condition of the cleaning liquid by a detection signal indicating the quantity of contaminative particles exceeding a predetermined upper limit value. It is also possible to inform the operator that the quantity of contaminative particles contained in the cleaning liquid is not greater than the predetermined upper limit value and the normal cleaning process can be achieved.
The cleaning method of the present invention may further comprise a step of cleaning workpieces by immersing the same in the cleaning liquid contained in the cleaning tank after it is decided on the basis of a detection signal provided by the control means that the cleaning liquid is appropriate to cleaning.
According to the present invention, the ability and the yield of the cleaning process can be improved by cleaning the workpiece after it is decided that the measured quantity of contaminative particles is not greater than the predetermined upper limit value indicating the upper limit of the quantity of contaminative particles for the cleaning liquid appropriate to cleaning.
The cleaning method of the present invention may further comprise a step of changing the cleaning liquid when the cleaning liquid change request signal is provided continuously by the control means for a time exceeding a predetermined time.
According to the present invention, the cleaning liquid is changed if the quantity of contaminative particles does not decrease below the predetermined-upper limit value in the predetermined time. Therefore, the ability and the yield of the cleaning process can be improved.
The cleaning method of the present invention may further comprise a step of changing the cleaning liquid when a differential particle number between the measured contaminative particle number of the cleaning liquid sampled before a start of a first cleaning cycle and that of the cleaning liquid sampled after the completion of a cleaning cycle exceeds a predetermined upper limit value.
According to the present invention, the cleaning ability of the cleaning liquid is improved and the yield can be improved because the cleaning liquid is changed when the differential particle number, i.e., the difference between the measured contaminative particle number of the cleaning liquid sampled before the start of the first cleaning cycle and that of the cleaning liquid sampled after the completion of the cleaning cycle, exceeds the predetermined upper limit value.
The cleaning method of the present invention may further comprise a step of comparing the measured contaminative particle concentration of the cleaning liquid sampled before a start of a cleaning cycle and that of the cleaning liquid sampled after the completion of the cleaning cycle, and providing the detection signal when a differential particle number between the respective contaminative particle numbers of the cleaning liquid, exceeds a predetermined upper limit value by the control means, and changing the cleaning liquid when the detection signal is provided by the control means.
According to the present invention, the cleaning ability of the cleaning liquid is improved and the yield can be improved because the cleaning liquid is changed when the differential particle number, i.e., the difference between the measured contaminative particle number of the cleaning liquid sampled before the start of the cleaning cycle and that of the cleaning liquid sampled when the completion of a cleaning cycle, exceeds the predetermined upper limit value.
The cleaning method of the present invention may change the cleaning liquid after the cleaning liquid has been used for a predetermined number of cleaning cycles or for a predetermined time.
According to the present invention, the cleaning ability of the cleaning liquid is improved and the yield can be improved because the cleaning liquid is changed when the same has been used for the predetermined number of cleaning cycles on the basis of experimental data or for the predetermined time determined on the basis of experimental data.